Tumor associated fetal antigens (TAFA) are being isolated and purified from chemically (methylcholanthrene) and virally (murine sarcoma virus) induced tumors. Affinity chromatography and isoelectric focusing are utilized to obtain TAFA for immunobiological characterizations. Topics currently being investigated include: identification of the sites of production of TAFA in syngeneic 13-15 day embryos; examination of the kinetics of TAFA expression in synchronized cells; and determination of the relationship between oncornavirus replication and TAFA expression. These studies are providing information about the physical-chemical properties of TAFA, and reagents generated by these studies are being utilized to develop specific immunological probes for investigations of the role of TAFA in modulating host immune responses. This systematic approach will generate information regarding select fundamental properties of the transformation process which may be associated with TAFA expression.